In a typical aromatic alkylation process, an aromatic compound is reacted with an alkylating agent, such as an olefin, in the presence of acid catalyst. For example, benzene can be reacted with ethylene or propylene to produce ethylbenzene or cumene, both of which are important intermediates in the chemical industry. In the past, commercial aromatic alkylation processes normally used AlCl3 or BF3 as the acid catalyst, but more recently these materials have been replaced by molecular sieve-based catalysts.
Aromatics alkylation processes employing molecular sieve-based catalysts may be conducted in either the vapor phase or the liquid phase. However, in view of the improved selectivity and decreased capital and operating costs associated with liquid phase operation, most commercial alkylation processes now operate under at least partial liquid phase conditions. Unfortunately, one disadvantage of operating under liquid phase conditions is that the molecular sieve-based catalysts tend to be more sensitive to the presence of catalyst poisons in the feed streams, especially those with a compound having at least one of the following elements: nitrogen, halogens, oxygen, sulfur, arsenic, selenium, tellurium, phosphorus, and Group 1 through Group 12 metals. Such impurities reduce the acid activity of such molecular sieve-based catalyst and hence decrease the cycle time between required regenerations of such catalyst.
The use of guard beds to remove trace contaminants from hydrocarbon feed streams is well known in the art. This is especially true for petrochemical and specialty chemical operations where product purity is critical. Normally, guard bed materials that contain bentonite clay, kaolin clay, special activated aluminas or molecular sieves are used and are placed upstream of a reaction vessel containing an acidic molecular sieve-based catalyst. These guard bed materials trap impurities in the feed streams so that product purity specifications can be met and poisoning of such catalyst can be reduced. However, such guard bed materials have limited capacity to adsorb impurities from aromatic feed streams to the low levels required for use in liquid phase alkylation processes which employ acidic molecular sieve-based catalysts. Therefore, a need exists for a guard bed material with an increased capacity to adsorb impurities more effectively. It is desirable to remove such impurities from the feed streams to such aromatic alkylation processes and thereby reduce the deactivation of the downstream acidic molecular sieve-based catalyst used in alkylation and/or transalkylation reactions.
According to the present invention, it has now been found that the capacity to adsorb catalyst poisons of a guard bed material, as measured by collidine update at 200° C., may be increased by a method in which an untreated guard bed material is dried with a drying gas at a temperature of greater than 200° C. to produce the treated guard bed material. Optionally, the guard bed catalyst may be contacted with water or humid gas prior to being dried. The treated guard bed material may be used to remove impurities from untreated feed streams to aromatic alkylation processes, thereby increasing the cycle length of such catalysts.